Measurements of longitudinal stresses in moving metal bands and devices therefor

ABSTRACT

A DEVICE FOR MEASURING LONGITUDINAL STRESSES OCCURRING ACROSS MOVING METAL BANDS UNDER LONGITUDINAL TENSION BY MEANS OF A DEFLECTING ROLLER CARRYING MEASURING DISCS. THE DEFLECTING FORCES ARISING IN THE CENTER OF THE BAND AND AT BOTH EDGES ARE MEASURED. THESE DEFLECTING FORCES ARE PROPORTIONAL TO THE TENSILE STRESSES.

Jan. 26, 1971 w. MUHLBERG 3,557,514 MEASUREMENTSOF LCNGITUDINAL STRESSES IN MOVING METAL BANDS AND DEVICES THEREFOR Filed Jan. 23, 19757Y 2 sheets-sheet z 737/ 7574 7j 7 7h 7g 7f FQ 6 MM35/wh United States Patent O 3,557,614 MEASUREMEN TS F LON GITUDINAL STRESSES IN MOVING METAL BANDS AND DEVICES THEREFOR Wolfgang Mhlberg, Gertrudisstr. 9, Krefeld-Bockum, Germany Filed `Ian. 23, 1967, Ser. No. 611,141 Claims priority, application Germany, Jan. 25, 1966, 1,573,698; Oct. 28, 1966, 1,573,716 Int. Cl. G01] 5/10 U.S. Cl. 73-144 3 Claims yABSTRACT oF THE DISCLOSURE A device for measuring longitudinal stresses occurring across moving metal bands under longitudinal tension by means of a deflecting roller carrying measuring discs. The deflecting forces arising in the center of the band and at both edges are measured. These deflecting forces are proportional to the tensile stresses.

Upon rolling, especially cold rolling of very thin metal bands of diicultly workable or deformable material, tensile stress (or strain or tractive force) is imparted thereto, before and behind the roller gap in the mill wherein the material is worked, primarily by the pressure of the rollers. This stress not only influences the guidance of the bands, but also the deformation of the bands in the direction of the rolling process. The inlluence of the deformation becomes the more important the thinner band to be rolled and the more the cold work hardening of the material increases, caused by the deformation process.

The rolling process thereby is rendered more diicult, and it generally is attempted to compensate for this difficulty by applying high tensile stresses, acting in the direction of the rolling process. 'I'he magnitude of these longitudinal stresses, however, of necessity is limited in practice to approximately to `30% of the working or deformation strength attained, in order to avert rupture of the bands. The reason for the application of these comparatively low tensile stresses is found in the fact that their distribution over the Width of the band is uneven. ;For instance, if the band is stretched more on the edges than in the center (which occurs due to the use of rolls with a high crown or due to too much heat in the center of the roller body thus providing a greater diameter), the tensile stresses shift dangerously towards the edges with constant pulling force and simultaneous decrease of the tensile stresses in the center of the bands. Under the most unfavorable conditions, this uneven distribution may provide tensile stresses in the edge regions which amount to thrice the average calculated value, if considered evenly distributed, while the center region attains a tensile stress of a zero value so that center ripples do not form and no indication of this uneven distribution of the stresses is present. At the edges, therefore, a tensile stress of approximately 75-90% of the deformation strength attained prevails. The difference from the stretch-strain limit or deformation strength thereby is too slight to prevent rupture of the band. If central ripples -do form on the bands, the stress at the edges is even higher and the peril of rupture of the band correspondingly greater.

The invention utilizes the well known fact that a moving metal band under longitudinal tension, when slightly i ce deflected from the direction of its movement by a roller, generates a corresponding deflecting force which acts as a load on the deflecting roller. This load is measured by permitting measuring discs, disposed on the deflecting roller, to act on the center and both edges of the band, as will be explained in detail herein'below. The measurements are transmitted to an indicating instrument, known per se, and read therefrom.

The embodiments of the invention will be illustrated with reference to the accompanying drawings. However, it should be understood that these are given merely by way of explanation, and not of limitation, and that changes may be made in the details without departing from the spirit and the scope of the invention as hereinafter claimed.

In the drawings,

FIGS. l and 2 are elevations of two embodiments of deilecting rollers provided with measuring discs;

FIG. 3 is a cross section of the roller shown in FIG. 2;

FIG. 4 is a cross section of a measuring disc;

FIG. 5 is a cross section of another embodiment of a deecting roller;

FIG. 6 is an elevation of the roller shown in FIG. 5;

FIG. 7 is a cross section of still another embodiment of a deilecting roller; and

FIG. 8 is an elevation of the roller along lines E-E of FIG. 7.

Referring now to these drawings, to ascertain the longitudinal stresses of a moving metal band across its width b, the deflecting roller 1 according to FIG. 1 is formed as a measuring roll wherein a common fixed shaft carries a plurality of small measuring discs la-lj, having equal shaft length, and the inactive roller parts 1k and `1l of dilerent shaft length. Opportunely, according to FIG. 1, the active and inactive roller parts are disposed asymmetrically about the centrally located disc 1a, whereby corresponding measuring means simultaneously must be present for the support forces A and B of shaft 2 which acts as a beam with two supports.

If the measuring means indicate equal support forces A and B, the longitudinal stresses across the moving band are distributed symmetrically, so that the partial load resulting from the longitudinal stress therein present, leads to a corresponding signal at the measuring instrument connected to measuring disc `:1a.

An asymmetrical distribution of the tensile stresses of the moving band across the band causes support forces A and B of different magnitude. These forces can be equalized, eg., in a strip mill frame, by tightening of one set screw and simultaneous loosening of the opposite screw thus shifting the longitudinal stresses caused by the differential lengthening of the band. Hence, it suffices to distribute the active and inactive roller parts according to FIG. l. It is, of course, also possible to distribute the measuring discs symmetrically over the roller or to provide the shaft 2 exclusively with measuring discs. Of the measuring discs 1a to 1j in FIG. 1, only three are connected to a measuring instrument, namely the one in the center of the band and those which just fully cover the edges.

Thereby the value at the band edges is not ascertained and compared to the value at the center, but the value in the corresponding edge area. However, the value at the edge can be calculated or deducted and the necessary countermeasures taken to reestablish the even distribution of the tensile stresses in the band. The measuring instruments connected with the measuring discs 1a and 1h, respectively, then indicate equal values.

It also suffices to install only one measuring disc adjustably relative to the width of the band, in the center of the deflecting roller or near one of its edges, respectively. This disc, through the measuring instrument connected to it, indicates the defiecting force apportioned to it which is proportional to the tensile stress in the course of this disc.

A preferred embodiment of a measuring disc is shown in FIG. 4. The disc consists of a casing 11 which is disposed on a roller bearing having an inner ring 9 and an outer ring 10. The former is disposed on the stationary shaft 2 and exerts pressure on a measuring beam 5, forming a fitting. An extensometer strip 8 is fastened to beam 5, e.g., by means of an adhesive. Measuring beam 5 has two support points -6 and 7. The wires from the measuring instrument to beam 5 are conducted through conduit 4 and central bore 3, by way of amplifiers. The measuring instrument can be any one of conventional devices and is not shown in the drawings, nor are the amplifiers. The deflecting roller carrying individual discs might not be usable in certain instances, for instance, when grooves are generated on the moving metal band, rounding of the edges of these discs notwithstanding. Formation of such grooves detracts from the quality of these bands. To obviate this, the deflecting roller carrying the discs 1a to 1l is provided with a thin-walled jacket 13 which is shrunk or pressed onto it. Thus, the roller has a closed jacketed surface, as also shown in FIG. l. Being thin-walled, this jacket does not jeopardize the technological advantages of the direct measurement of the deflecting forces in the paths of the discs 1a to 1]' which are proportional to the prevailing tensile stresses, because the measuring error due to the load distributing effect of the jacket 13 is negligible. Moreover, the salient feature is the comparison of the tensile stresses in the center of the band with those at the edges.

The effect of a closed roller surface also is attained by deilecting the band by a solid or hollow roller 12 of small diameter, as shown in FIGS. 2 and 3. This roller 12 is supported by a plurality of measuring discs 1a to 1j and 1b also by the terminal discs 1k and 1k', acting as a beam propped by several supports. By pinning the roller 12 down at both ends by means of bearings 15 (for instance roller bearings), the roller is fixed in the working plane by the forces F1 and F2. The individual measuring discs 1a to 1j and 1b respectively, advantageously have a slight, concentrically ground, crown so that roller 12 only touches their central planes. This effects precisely defined support distances for the deflecting roller 12 which is a continuous beam. Here again, by suitable construction of roller 12, the comparison of the loads determined by discs 1a to 1j and 1b in the center and at the edges facilitates deduction of the tensile stresses across the moving band.

If roller 12 is of adequate volume, it sufiices to prop the same at both ends and in the center on rotatable measuring discs and to determine the support forces which are an exact measure of the distribution of the tensile stress across the traveling band.

A variation of this measuring arrangement is illustrated in FIGS. 5 and 6. Here, a solid or hollow deflecting roller 12 is supported, throughout its length, in a saddle formed by two rows of offset measuring discs 1f to lq. These discs are disposed on the stationary shafts 2a and 2b. Additional support of roller 12 at its ends merely serves to fasten the same and to prevent unintended lifting.

Again, it sufiices to support a roller 12 of adequate v01- ume by saddles in the center and at both ends, in the manner described and shown in FIGS. 5 and 6, or in a similar manner, and to determine the support forces of the beam traversing two equal sections in order to determine the distribution of the tensile stress. It even suffices to support the roller 12 of adequate volume at both ends in pressure pickup boxes and in the center by a rotating measuring disc to attain this determination.

The advantage of a saddle support of the actual roller 12 can be combined with the advantage of a direct measurement of the distribution of the tensile stresses when the arrangement according to FIG. 1, consisting of a plurality of discs and a shrunk-on or pressed-on thin-walled jacket, is so modied as is shown in FIGS. 7 and 8.

In the embodiment, the measuring roller 12 is constructed as a hollow roller consisting of the supporting rings of equal dimensions 1f to 1j, terminal rings 14, accommodating the roller bearings 1S, and a superposed thin-walled tube 13 having a slight shrink fit. This hollow roller 12, by means of its bearings 15, is supported on a continuous shaft 16 which, in turn, is fastened in bearing 20. The means 21 permit adjustment of the distance of measuring roller 12 from solid or hollow support rol]- ers 2a and 2b, which forms a saddle. The local load of the defiecting roll, due to the locally prevailing tensile stress a' of the moving band, is determined as the deformation of the supporting rings 1f to 1j by measuring the radial distance of their internal curvatures from the shaft 16. According to a preferred embodiment conforming to FIGS. 7 and 8, these changes in the radial distances of the internal curvatures can be determined as the changes of the air gap of the U-shaped magnets 18]c to 18j, assigned to each of the supporting rings. The wiring for these magnets 18f to 18]' is conducted through the central conduit 17 and the channels 19j to 19j, assigned to these magnets.

The changes in the radial distance of the internal curvatures of support rings 1f to 1j which, disregarding the negligible load-distributing effect of the thin-walled tube 13, constitute a measure of the locally prevailing tensile stress in the band, also can be determined with the aid of any other suitable instrument of electrical, optical or pneumatic nature.

In lieu of the saddle-like support of measuring roller 12, linear seating can be chosen, according to FIGS. 2 and 3. By adapting the angle of deflection to the thickness and the tension (or traction), the optimal measuring effect can be attained.

Another way of measuring the distribution of the tensile stresses across a moving metal band under longitudinal tension is to construct the deflecting roller in the form of a plurality of small rollers which preferably are seated in individual forks. These small rollers, defiecting the band to an equal extent, are put under load in correspondence to the tensile stress in their respective paths so that differential loads in the distribution of the stresses effect different load on the individual rollers. Only the deflecting forces of the rollers in the center of the band and those just fully covering the band edges are measured.

I claim as my invention:

1. A device for the measurement of longitudinal tensile stresses in a moving metal band under longitudinal tension which comprises a detlecting roller consisting essentially of a continuous shaft, a plurality of like supporting rings about said shaft, and a thin-walled jacket about said rings; a bearing at each end of said shaft; two support rollers below said deliecting roller, forming a saddle therefor; said supporting-rings deforming under the loading of said dellecting roller by the moving band; and measuring means responsive to the change in the radial distance of the internal curvatures of said rings from said shaft caused by the deformation for measuring the prevailing tensile stresses.

2. A device according to claim 1 wherein said meas uring means comprises a U-shaped electromagnet adjacent the internal curvature of each of said rings, said change n radial distance effecting a change in the air gap of said electromagnet.

3. A device for the measurement of longitudinal tensile stresses in a moving metal band under longitudinal tension which comprises; a deflecting roller across the width of said band, said deflecting roller consisting essentially of a continuous shaft, a plurality of like supporting rings about said shaft, and a thin-walled jacket about said rings; a bearing at each end of said shaft; two support rollers below said deecting roller, forming a saddle therefor; means interposed between said deecting roller and said support rollers for adjustment of the distance therebetween; said supporting rings deforming under the loading of said deecting roller by the moving metal band; and measuring means responsive to the change in the radial distance of the internal curvatures of said measuring the prevailing tensile stresses.

References Cited UNITED STATES PATENTS Garrett et a1. 73-159 Kaestner 73-159 Hull et al. 73-144 Martin 73-144X Flinth 73-144 0 CHARLES A. RUEHL, Primary Examiner 

